Is the Network Render addon able to render with openGL?
AFAIK netrender doesn't support this, as there is no opengl "render engine" defined in blender (as you noted). There is an opengl render operator, but it is not defined as a formal render engine.

However there is a simple alternative approach you might be able to use. See the following questions:


Render on more than one computer?
Cycles Netrender Returning Black
How to use baked fluid with network render?